Bounded-Error Log

This is a Corral puzzle in which half the clues are multiplicative. For each symmetric pair of clues, one is normal and one is multiplicative.

Okay did I mention how I sucked at the command line? This is part of the journey towards stopping. Yes, I’m on a Mac and it’s not very *nix-y in some ways but it’s enough for me for now.

Today’s story starts when I learned about gdb, the pure-command-line GNU Debugger, which is incredibly cool. I have tried and failed to learn how to use the debug function on many of my IDEs; I found shotgunning printf statements as needed faster. This may well be the first time I found a command-line tool so much more intuitive than the GUI-equipped programs. Wow.

Then I learned that for some reason the gdb on this computer was 6.3, which is 1.2~1.5 major versions behind (depending on how you count) and missing a frustrating amount of features. (The one that the current Code::Blocks installer installs is also something like 6.4. Blech.)

Why do so many people have these three- or four- or even five-digit inbox unread counts? I become uncomfortable when I have more than about five unread emails, or if there are twenty emails of whatever status in my inbox — the rest get archived, of course. Out of sight, out of mind. Whew. It’s hard for me to fathom how anybody can sleep knowing they have such a scary number of unread emails waiting for them.

Why does the status of being unread matter, one might ask? There are already so many ways to classify things in the typical inbox: stars or labels or folders or flags or whatever your mail service may call them. Well, the thing that makes the unread qualifier stand out is that it already has meaning; you don’t need to assign it any. It means you haven’t read it! Thank you, Captain Obvious.

If you know how to use email, there are no good reasons to ignore the status. Is the email actually not important to the point where you won’t even bother to read it? In that case, why is it even in your inbox? If it’s spam, mark it as such; spam filters are pretty effective nowadays, but only if you train them, and even if not it only takes one click to get rid of it. If it’s some notification you don’t care about, unsuscribe or fine-tune your subscription. As invasive as web services are getting nowadays, I haven’t yet seen a legitimate one that doesn’t provide a link to let you do one of these things, even if it’s concealed in small gray text at the bottom of the email. Should you encounter a notification that doesn’t have these links or doesn’t stop spawning evil clones after you tell it to, don’t think twice; it is spam and should be mercilessly filtered as such. And if you still have two hundred emails left after all that, you should either rethink your values or start reading them now.

This is a Fillomino puzzle where every polyomino is required to be nonrectangular (which also bans squares). Write a number in every empty cell so that every group of cells with the same number that is connected through its edges is a shape that’s not a rectangle with that number of cells.

Fillomino-Fillia 2 is coming! Anyway I don’t know how to judge difficulty but this is probably terrible practice. I should try a Skyscrapers if I can keep pretending USH homework doesn’t exist which I probably shouldn’t.

Nice and tricky. (I think.)

In fact I tried to be too tricky and spent a very long time fixing an ambiguity. It was worth it though.

LITS - Nikoli. Exactly one tetromino per region, no 2x2s, they’re connected, adjacent tetrominoes are noncongruent.

Stopped by a friend’s house a few days ago to do homework, which somehow devolved into me analyzing what programming language I should try to learn next in a corner, which is completely irrelevant to the rest of this post. Oops.

Anyway, in normal-math-curriculum-land, my classmates are now learning about matrices. How to add them, how to multiply them, how to calculate the determinant and stuff. Being a nice person, and feeling somewhat guilty for my grade stability despite the number of study hours I siphoned off to puzzles and the like, I was eager to help confront the monster. Said classmate basically asked me what they were for.

Well, what a hard question. But of course given the curriculum it’s the only interesting problem I think could be asked.

When I was hurrying through the high-school curriculum I remember having to learn the same thing and not having any idea what the heck was happening. Matrices appeared in that section as a messy, burdensome way to solve equations and never again, at least not in an interesting enough way to make me remember. I don’t have my precalc textbook, but a supplementary precalc book completely confirms my impressions and “matrix” doesn’t even appear in my calculus textbook index. They virtually failed to show up in olympiad training too. I learned that Po-Shen Loh knew how to kill a bunch of combinatorics problems with them (PDF), but not in the slightest how to do that myself.

Somewhere else, during what I’m guessing was random independent exploration, I happened upon the signed-permutation-rule (a.k.a. Leibniz formula) for evaluating determinants, which made a lot more sense for me and looked more beautiful and symmetric

\[\det(A) = \sum_{\sigma \in S_n} \text{sgn}(\sigma) \prod_{i=1}^n A_{i,\sigma_i}\]

and I was annoyed when both of my linear algebra textbooks defined it first with cofactor expansion. Even though they quickly proved you could expand along any row or column, and one also followed up with the permutation formula a few sections later, it still felt uglier to me. Yes, it’s impossible to understand that equation without knowledge of permutations and their signs, but I’m very much a permutations kind of guy. Sue me.

That’s not a picture. Why is it recreated as one? Oh well.

You can interpret this as me about reaching level 8.1 (the user ranking) on rankk or complaining about how infuriating level 8.1 (the puzzle) is. I’m torn.

This is one of a bunch of MellowMelon’s Double Backs. Briefly, draw a closed loop through all square centers visiting each bold-outlined area twice. Shaded cells do not influence solving, only aesthetics.

Most uncreative picture ever! But it’s suitable after CiSRA’s Puzzle Week. This might be the first time our AoPS team managed all four puzzles in a group.

…sigh, now I must handle the guilt for squeezing out so much time from my normal schedule.

This is one of a bunch of MellowMelon’s Double Backs. Briefly, draw a closed loop through all square centers visiting each bold-outlined area twice. Shaded cells do not influence solving, only aesthetics.

Right, back to puzzles because I have nothing substantial to say. Circumstantial evidence suggests I created this one in June.

This is one of a bunch of MellowMelon’s Double Backs. Draw a closed loop through all square centers visiting each bold-outlined area twice.

Too lazy to explain rules today although this is probably an easy one.